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Show 178 EXPLORATION OF TDE OARONS OF TIIE COLORADO. mountain is composed of sedimentary beds, and the summit of this, cooled Java. So oven, theso so called eruptive mount<tins were not piled up, but were carved from beds of sedimentary and igneous matter. We have named this group, in honor of the Secretary of the Smithsonian Institution, ''llenry Mountains." A few miles below the mouth of the San Juan River we come to an interesting monoclinal fold, where the dip of the rocks is in a direction a little north of cast; that is, tho beds are dropped down on the ~astern side of the line, which trends nearly north and south, not broken off and dropped down, but flexed, or bent, so that the beds on the western side of the line are found at an altitude many hundreds of feet above those on the east, and farther down the river the rocks exposed at the water edge are of greater age than those above. llereaftor, in this discussion, I shall more fully explain the nature of tl~ese m.o~oclinal folds and faults, and the topographic features to which they gtve or1gm. At the foot of this cafion another mouoclinal fold is seen, with the thrm~, or drop, also on the east side, or the uplift, if one is so pleased to term .It, on the west side; and this brings up again Carboniferous sandstones and lir~lCstones. The surface of the country immediately outside the canon, alon~ Its ":hole course, is on the summit of the red Trias; but, away back ~n eithe~ Sid~, we ~ee long lines of towering cliffs, now running in this, now ~~ that d1rectwn, still keeping their courses parallel to the axes of folds h' h . tt d. . W IC med se·a ere m man. y dtrections over the country· A reg.w n more d esoI ate, an ' for .all econoDllc purposes, more valueless, perhaps, cannot be found on the continent. There are some features of this cafion of great interest whi 1 I h already mentioned in the account of the exploration Th ' Chl have b {I d ( · eso are t e c am- ~~s, ohr ca~es, oun along the canon, at the foot of the wall, hero and there or m t e side canons and gulches . the great mu . I I' f:i! b . ' . f 1 · ' Ia c Ius, a out sweepmg cmves o t le river; ten-aced glens wh th II d ·fi d . ' ere e wa s are composed of well . e ne strata, With springs about which k d d oa s an aspens grow· and tl e eep, narrow alcoves or side gulches. ' l The origin of these chambers was explained in the mention of Music OANONS IN TllE SANDSTONE. 179 Temple. They are due to the crumbling of softer rocks, which underlie harder beds, the friable material being carried away by springs, or wet weather streams. The greater number aro found at the heads of littlo gulches. In many places the walls of the canon are of homogeneous sandstone, and where the river sweeps in a great curve at tho foot of the wall, mural cliffs are found. The oak glens have been excavated by springs, and the alcoves are tho channels of intermittent rills. Away from the river, on either side, there are broad stretches of na~ed sandstone, carved by the rains into gentle billows or mounds. As the rams gather into streams, the little valleys, or grooves, between the mounds become gulches, and where the smaller streams gather into larger tho gulches become canons, often having vertical or even overhanging walls. When, in the progress of corrasion, these streams have c~t through harder beds, and reach softer, the channels are seen to w1den. The manner in which this wideni'Bg occurs is curious. The streams are everywhere tortuous, and, as the power of the water is constantly exerted in corrasion, the streams are not only made deeper, but the curves arc incref}.sed by methods well known to those who have studi.ed the origin an~ change of river channels; so the walls are often undermmed on the outm side of curves and here overhanging cliffs are found. So these 'canons are not only flexuous in horizontal outline, but they are also flexuous in vertical outline, giving them warped or tortuous ~om·ses. The streams do not always cut channels with vertical walls. Occaswnally, deep water-ways are found, with flaring walls to th~ very bott.om. Such canons usually occur where the beds of streams are m rocks qmte as har~, or even harder, than those above. A good illustration of such a channel Is seen 1· n Fw' ure 48 . Bosi'des the grooves ' crulches, and canons that head o th 0 among e mou nds , we have (a nother class of water-ways, to .w hich the form. er are someti·m es t r1'b u t ary. Many streams come down from d1stant mountams, where they receive a more constant supply of .water. They o~te.n run for many miles throucrh narrow, winding cm10tiS, w1th walls so preC1pltous that h t b 0 t ey canno e sea1 e d , and they form impassable barriers to the traveler. |
